JP2022170736A - separation membrane - Google Patents

Abstract

To provide a separation membrane which prevents clogging and can obtain a permeation liquid having excellent flavor.SOLUTION: A separation membrane has a layer having a spherical structure, wherein the spherical structure contains a polyvinylidene fluoride-based resin, a thickness L of the layer is 60 μm or more and 500 μm or less, the layer has a first surface and a second surface, an existential quantity Pmax/Pmin of a region Spmax with a maximum existential quantity of a polysaccharide component to a region Spmin with a minimum existential quantity thereof in a polysaccharide closed state obtained by a polysaccharide closed test in the regions partitioned with a width of 5 μm in a film thickness direction is 100.8 or more and 102.5 or less, seven or more regions with a width of 5 μm exist between the Spmax and the Spmin, and the Spmax is a region close to the first surface than the Spmin.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a separation membrane that is resistant to clogging during filtration of fermented liquid using a membrane module in the fermentation industry, food industry, etc., and has excellent durability against chemical cleaning.

In the treatment of fermented liquid in the food industry, diatomaceous earth was conventionally used to remove yeast, solids, colloids, etc. in beer and wine after fermentation. cannot be incinerated, and there is a problem of high disposal costs due to the large amount of use. Therefore, in recent years, attention has been paid to the treatment of fermented liquid using separation membranes, such as ultrafiltration membranes and microfiltration membranes, which are excellent in miniaturization of devices.

When fermented liquids such as beer and wine are processed in a separation membrane module, a layer consisting of removed microorganisms, their crushed products, colloids, etc. is formed on the membrane surface, clogging the membrane and increasing the filtration pressure. There is a problem that the separation membrane tends to cause an increase in the filtration rate and a decrease in the filtration rate over time, that is, the fouling of the separation membrane tends to occur.

As a membrane structure that prevents clogging of the membrane surface and exerts filtration performance, the surface pore size of one side of the separation membrane is larger than the substance to be removed, and the minimum pore size layer is placed on either the surface of the other side or the membrane part. A membrane capable of so-called depth filtration, in which impurities are captured inside the membrane, has been developed (Patent Document 1).

Furthermore, Patent Documents 2 and 3 disclose a hollow fiber membrane for beer filtration containing a hydrophilic polymer and having an asymmetric structure.

WO2016/006611 WO2016/182015 WO2017/155034

In recent years, in the filtration of beverages, there is an increasing demand not only for clogging resistance but also for improving the flavor of the permeated liquid.
INDUSTRIAL APPLICABILITY According to the present invention, a separation membrane that is less prone to clogging during filtration of a fermentation liquid using a membrane module in the fields of the fermentation industry, the food industry, etc., and is capable of obtaining a permeate having an excellent flavor. is provided.

As a result of intensive studies, the present inventors found that the above-described problems can be solved by a separation membrane in which the clogged state is within a certain range when the polysaccharide aqueous solution is filtered and clogged by a predetermined method, and the present invention has been completed. reached.
The present invention has any one of the following configurations [1] to [3].

[1] A separation membrane comprising a layer having a spherical structure, wherein the spherical structure contains a polyvinylidene fluoride-based resin and the layer has a thickness L of 60 μm or more and 500 μm or less, and the separation membrane has a first surface and a Region Sp having the second surface and having the largest amount of polysaccharide components in the polysaccharide clogging state obtained in the following polysaccharide clogging test, among the regions separated by a width of 5 μm in the film thickness direction in the cross section of the separation membrane The polysaccharide component abundance ratio P _max /P _min in the region Sp _min that is the minimum of _max is 10 ^0.8 or more and 10 ^2.5 or less, and the 5 μm wide region is 7 or more between Sp _max and Sp _min A separation membrane that is present and in which Sp _max is a region closer to the first surface than Sp _min .
Polysaccharide occlusion test: An aqueous solution containing 2.0% by weight of a water-soluble polysaccharide component having an average dispersion diameter of 100 nm or more and 1000 nm or less and 5.0% by weight of ethanol was applied to the first surface at 2.0 m ³ /m ² /day. Filtration is performed at a constant flow rate by supplying to , and the filtration is stopped when the transmembrane pressure difference becomes 10 times the initial transmembrane pressure difference.

[2] Among the regions where the abundance ratio of the polysaccharide component is less than 3 × P _min , the region closest to the first surface is Sp _(min−1) and Sp _max , and there are five regions at intervals of 5 μm The separation membrane according to [1], comprising the above.

[3] Among the above regions, the heat of fusion ratio Q _max /Q _min in the region Sq _max where the heat of fusion Q _i is the maximum and the region Sq _min where the heat of fusion Q i is the minimum expressed by the following formula (1) is 2.0 or more and 50.0 and
The separation membrane according to [1] or [2], wherein seven or more 5-μm-wide regions exist between Sq _max and Sq _min , and Sq _max is a region closer to the first surface than Sq _min .

dq _i /dt: Differential scanning calorimetry change per volume in region _Si (J/K/cm ³ )
t: scanning temperature (K)

INDUSTRIAL APPLICABILITY According to the present invention, a separation membrane is provided in which clogging is less likely to occur during filtration of a fermented liquid using a membrane module in the fields of the fermentation industry, the food industry, etc., and the permeated fermented liquid has an excellent flavor. be.

<Separation membrane>
(1) Spherical Structure Layer The separation membrane of the present invention is a porous membrane and includes a layer having a spherical structure (hereinafter referred to as "spherical structure layer"). The spherical structure contains a polyvinylidene fluoride-based resin, and the thickness L of the spherical structure layer is 60 μm or more and 500 μm or less. Another layer may be provided on at least one surface of the spherical structure layer. That is, the separation membrane may have two or more layers.
When the thickness is 60 µm or more, a separation membrane having sufficient strength for filtering the polysaccharide aqueous solution can be obtained. Further, when the thickness is 500 μm or less, a sufficiently large membrane area can be obtained when a membrane module is produced by filling the separation membrane.

A spherical structure is a spherical resin, which is connected to each other to form a porous structure.

(2) Occlusion property of polysaccharide In the separation membrane of the present invention, the polysaccharide component exhibits a specific distribution in the film thickness direction by the polysaccharide occlusion test.

In the polysaccharide clogging test, a 5.0 wt% ethanol aqueous solution containing 2.0 wt% of a water-soluble polysaccharide component having an average dispersion diameter of 100 nm or more and 1000 nm or less was applied to the first surface of the separation membrane at 2.0 m ³ /m ² /day. Filtration is performed at a constant flow rate by supplying to , and the filtration is stopped when the transmembrane pressure difference becomes 10 times the initial transmembrane pressure difference. Further, after passing about 1.0 L/m ² of pure water, a sample is cut out using a single-edged razor, and the cross section is cleaned by argon gas cluster ion beam etching.

The abundance of polysaccharide components in the thickness direction of the membrane can be evaluated based on the following time-of-flight secondary ion mass spectrometry (TOF-SIMS).

TOF-SIMS measurement of the film thickness cross-section, and from the measured mass spectrum, the peak value derived from the polysaccharide component normalized by the characteristic peak of the separation membrane before the test was calculated, and the line profile in the thickness direction was drawn. do.

Assuming that the rising position of the peak intensity derived from the separation membrane is 0, the line profile is divided every 5 μm in the thickness direction, and region names are assigned in order from S1. The average value of the polysaccharide component peak values in each region is taken as the amount of polysaccharide components present in the polysaccharide obstruction state.

Calculation of the abundance ratio will be described below, but the logarithmic value mentioned here refers to a common logarithmic value with a base of 10 unless otherwise specified.

When the abundance of the regions Sp _i is P _i , the logarithm value Log(P _max /P _min ) of the abundance ratio between the region Sp _max having the largest abundance and the region Sp _min having the smallest abundance is 0.8 or more. It is preferably 2.5 or less, and Sp _max is closer to the first surface than Sp _min . More preferably, the logarithmic value of the abundance ratio is 0.9 or more and 2.0 or less.

When the logarithmic value of the abundance ratio is 0.8 or more, a sufficient amount of the component to be blocked can be trapped inside the separation membrane (that is, a sufficient depth filtration effect can be obtained). In addition, when this value is 2.5 or less, a component that imparts a flavor can be permeated, so that a permeated liquid having a good flavor can be obtained.

Moreover, it is preferable that seven or more of the 5 μm regions exist between the maximum region Sp _max and the minimum region Sp _min . When the component to be blocked is captured by the separation membrane, the flavor component may also adhere to and be captured by the captured component. can be made

Furthermore, when Sp _min-1 is the region closest to the first surface in the region where the abundance ratio of the polysaccharide component is less than 3 × P _min , the 5 μm interval between Sp _max and Sp _min-1 is Preferably, there are 5 or more regions. By separating the two regions by 5 regions or more, a sufficient thickness of the interior of the separation membrane can be used to capture the components to be blocked.

(3) Water molecules When undiluted liquid such as fermentation liquid is filtered, the components of the fermentation liquid adhere to the walls of the channels inside the separation membrane. has a large impact. The wall of the channel is the inner wall of the pores in the porous structure of the separation membrane, and is composed of the surface of the spherical structure in the spherical structure layer.

Water molecules are generally classified into free water, intermediate water, and non-freezing water according to their mobility. Free water is water molecules in a state similar to bulk water that solidifies at 0°C. Intermediate water is water with a low melting point that solidifies at a temperature below 0°C due to interaction with the contact interface. Antifreeze water is a water molecule that does not solidify because of its extremely strong interaction with the contact interface.

The interaction of water molecules with the interface is modified by the new hydrophobicity and shape of the walls of the channels, resulting in reduced mobility of water molecules on hydrophilic surfaces and in narrow spaces where the distance between adjacent walls is less than 100 nm. Water molecules are physically constrained in the pores and their mobility is reduced.

In general, the adhesion of fermentation liquid components including yeasts, fungi and their products is suppressed on the surface where intermediate water having moderate motility is retained.

From the above mechanism, in the separation membrane, there is little intermediate water on the first surface and its vicinity in order to capture the components to be blocked, and there is much intermediate water on the second surface side to suppress clogging due to adhesion of the components to be permeated. is preferred.

Here, the amount of intermediate water in each region in the film thickness direction is determined by the heat of fusion per volume, and the heat of fusion per volume is the heat of fusion of intermediate water that melts at -15.0 to -0.1 ° C. is divided by the sample volume including voids (J/cm ³ ). The heat of fusion can be measured by differential scanning calorimetry.

When regions are divided at intervals of 5 μm in the film thickness direction, the ratio of the intermediate water content between two regions where the ratio of the intermediate water content in each region is maximum is preferably 2.0 or more and 50.0 or less. 2.5 or more and 10.0 or less are more preferable, and 3.0 or more and 5.0 or less are still more preferable. By setting the maximum value of the intermediate water amount ratio to 2.0 or more, it is possible to achieve both trapping and clogging suppression. When the maximum value of the intermediate water ratio is 50.0 or less, it is possible to moderately capture the components to be blocked in the low intermediate water region, and to moderately permeate the flavor components in the high intermediate water region.

(4) Composition of Separation Membrane The separation membrane preferably satisfies any one of (A), (B), and (C) below, more preferably satisfies any two, and satisfies all three. More preferred.

(A) The separation membrane is a porous membrane containing a hydrophobic polymer, and the average pore diameter at each position in the film thickness direction from the surface of the separation membrane in contact with the undiluted liquid to be filtered to the other surface becomes smaller. It has a progressive structure. In the region where the average pore diameter measured by the method described later is small, there are many pores that physically hold intermediate water relative to the void volume through which the fermentation liquid permeates, and the effect of suppressing the adhesion of components that you want to permeate is obtained. be done.
Here, the decreasing structure may be any change that can be substantially depth-filtered, and may be either a gradual change or a step-by-step change. It does not matter if a region that does not have

(B) The separation membrane is a porous membrane containing a hydrophobic polymer, and the specific surface area at each position in the thickness direction from the surface of the separation membrane in contact with the undiluted liquid to be filtered to the other surface increases. It has several structures. In a region with a large specific surface area, there are many pores that physically hold intermediate water relative to the void volume through which the fermentation liquid permeates, and an effect of suppressing the adhesion of components to be permeated is obtained.
Here, the increasing structure may be any change that can be substantially depth filtered, and may be either gradual change or stepwise change. It does not matter if a region that does not have

(C) The wall of the separation membrane channel is a porous membrane containing a hydrophilic polymer partially or entirely, and the wall of the channel is divided into three equal parts in the film thickness direction, region a of the channel wall comprising surface A in contact with, region c of the channel wall comprising the other membrane surface C, and region c of the channel wall between region a and region c When divided into the region b, the content ratio Ca of the hydrophilic polymer in the region a is smaller than the content ratio Cc of the hydrophilic polymer in the region c. In region c, there are many pores that chemically retain intermediate water, and the effect of suppressing adhesion of components to be permeated can be obtained.

Here, dividing the wall of the channel into three equal parts in the film thickness direction means that the thickness of each layer is in the range of 33±5 when the total film thickness is 100.

(5) Hydrophobic polymer In the present invention, the hydrophobic polymer is not limited as long as it dissolves in the hydrophobic organic solvent used for film formation. Examples of hydrophobic polymers include polytetrafluoroethylene, polyvinylidene fluoride, polylactic acid, polyhydroxyacetic acid, polycaprolactone, polyesters such as polyethylene adipate, polyurethanes, poly(meth)acrylates, polyvinylacetals, Single components such as polyamides, polystyrenes, polysulfones, cellulose derivatives, polyphenylene ethers, polycarbonates, etc., polymer alloys or blends of two or more selected from these, or copolymers of monomers forming the above polymers, etc. Examples include, but are not limited to, the above examples. Among these, as resin components excellent in heat resistance, chemical resistance, etc., fluorine-based resins such as polytetrafluoroethylene and polyvinylidene fluoride, or sulfone-based resins such as polysulfone and polyethersulfone can be mentioned. Among these resins, vinylidene fluoride resin is particularly preferable because it has high compatibility with the solvent and can easily prepare a uniform manufacturing stock solution. A vinylidene fluoride resin means a resin containing at least one of a vinylidene fluoride homopolymer and a vinylidene fluoride copolymer. The vinylidene fluoride resin may contain multiple types of vinylidene fluoride copolymers.

A vinylidene fluoride copolymer is a polymer having a vinylidene fluoride residue structure, and is typically a copolymer of a vinylidene fluoride monomer and other fluorine-based monomers. Examples of such a copolymer include a copolymer of one or more monomers selected from vinyl fluoride, ethylene tetrafluoride, propylene hexafluoride, and ethylene trifluorochloride and vinylidene fluoride. be done.

In addition, the weight average molecular weight of the vinylidene fluoride resin may be appropriately selected according to the required strength and water permeability of the separation membrane. descend. Therefore, the weight average molecular weight is preferably 50,000 or more and 1,000,000 or less. For water treatment applications in which the separation membrane is exposed to chemical cleaning, the weight average molecular weight is preferably 100,000 or more and 700,000 or less, more preferably 150,000 or more and 600,000 or less.

The separation membrane preferably contains a vinylidene fluoride resin as a main component, and the proportion of the vinylidene fluoride resin in the hollow fiber membrane is preferably 80% by weight or more, more preferably 90% by weight or more, and 95% by weight or more. is more preferable.

(6) Average pore size and specific surface area The structure of the separation membrane is not particularly limited, and it may be a symmetrical membrane with uniform pore size and porosity as a whole, or the pore size and porosity change in the thickness direction of the membrane. It may be an asymmetric membrane. Moreover, the separation membrane may be a composite membrane having a support layer for maintaining strength and a separation functional layer for separating target substances.

The separation membrane of the present invention preferably has pores with an average pore diameter in the range of 10 to 10000 nm. The average pore size of the pores is more preferably in the range of 50-5000 nm, still more preferably in the range of 100-3000 nm. When the average pore size is 100 nm or more, the permeation resistance is less likely to increase and the pressure required for filtration can be prevented from increasing. It is possible to prevent a decrease in filtration efficiency or the like from occurring. Moreover, sufficient fractionability is obtained as it is 3000 nm or less.

The pore diameter of communicating pores of 100 nm or more can be measured by mercury porosimetry. In the mercury intrusion method, a pressure p is applied to mercury so that the mercury is injected into the communicating pores of the separation membrane, and the volume change dV of the mercury in the cell with respect to the pressure increment dp is measured. , to obtain the pore size distribution function F(r).

(Here, r is the pore radius, σ is the surface tension of mercury (0.480 N/m), and θ is the contact angle (140°).)
The average pore size can be obtained by the following formula (3).

The pore size of pores, including non-communicating pores of less than 100 nm, can be measured by a gas adsorption method. For example, after removing water and the like adsorbed on the separation membrane, nitrogen gas adsorption measurement is performed at liquid nitrogen temperature, and the relative pressure (adsorption equilibrium pressure/saturated vapor pressure at liquid nitrogen temperature) of nitrogen up to 0.99 The average pore size of the separation membrane can be measured from the change in gas adsorption amount (converted to liquid).
The specific surface area of the pores is similarly measured by the above measurement.
As the shape parameters of the channel walls of the separation membrane that affect the amount of intermediate water, the average pore diameter and specific surface area obtained by the gas adsorption method are preferably employed.

(7) Hydrophilic polymer The hollow fiber membrane contains a copolymer composed of N types of monomer units, and the hydration energy density of the hydrophilic polymer is 40 to 70 cal mol ^-1 Å ^-3 . It is preferable that the hydrophilic polymer is included.

Further, the volume fraction of the monomer unit having the highest hydration energy density is 35 to 90%, and the difference in hydration energy density is 10 to 100 cal·mol ⁻¹ ·Å ⁻³ .

A "monomer unit" refers to a repeating unit in a homopolymer or copolymer obtained by polymerizing a monomer. For example, a hydrophobic monomer unit refers to a repeating unit in a homopolymer or copolymer obtained by polymerizing a hydrophobic monomer.

"Contains N types of monomer units" means that the copolymer contains N types of repeating units (ie, monomer units). N is an integer of 2 or more, and monomer unit i refers to any one of N types of monomer units. For example, a vinylpyrrolidone/vinyldecanoate random copolymer contains two types of monomer units, vinylpyrrolidone and vinyldecanoate.

"Copolymer" means a polymer composed of two or more types of monomer units.

"Hydration energy" means the energy change that a system undergoes when a solute is placed in an aqueous solution.

"Hydration energy of a monomer unit" means the absolute value of the value obtained by subtracting the energy of the monomer unit in vacuum from the energy of the monomer unit in water.

"Hydration energy density" means hydration energy per unit volume. For example, in the case of a monomer, it is a numerical value defined by the following formula (4).

The “monomer unit j having the highest hydration energy density” means a monomer unit having the highest hydration energy density defined by the above formula (4) among the monomer units constituting the hydrophilic polymer. .

The “monomer unit k having the smallest hydration energy density” means a monomer unit having the smallest hydration energy density defined by the above formula (4) among the monomer units constituting the hydrophilic polymer. .

Regarding the molecular model of the monomer unit, for example, when the monomer unit has the structure represented by the following chemical formula (I), the structure represented by the following chemical formula (II) is the object of calculation. That is, the carbon terminal on the side to which the side chain R is bonded is terminated with a methyl group ((a) in the following formula (II)), and the carbon terminal on the side to which the side chain R is not bonded is a hydrogen atom (the following formula (II ) using the structure terminated in (b)).

The energy in vacuum and the energy in water of the monomer unit in formula (4) can be calculated by the following methods.

First, the molecular model of the monomer unit is structurally optimized. For geometry optimization, density functional theory is used. We use B3LYP for functionals and 6-31G(d,p) for basis functions. Furthermore, set opt as a keyword to be described in the input file.

Next, energy in vacuum and energy in water are calculated for the optimized structure. Energy calculation in vacuum uses density functional theory. We use B3LYP for functionals and 6-31G(d,p) for basis functions. Energy calculations in water use density functional theory. We use B3LYP for functionals and 6-31G(d,p) for basis functions. Furthermore, in order to calculate the energy in water, we use the continuum dielectric model and use the following keywords.
SCRF = (PCM, G03 Defaults, Read, Solvent = Water)
Radii=UAHF
Alpha = 1.20
The hydration energy of the monomer unit is determined by obtaining the SCF energy in vacuum and water. Here, the SCF energy is the value of E written in the line labeled "SCF Done:".

Quantum chemical calculation software Gaussian09 (registered trademark) manufactured by Gaussian is used for the energy calculation.

In the hydrophilic polymer, the hydration energy density of the hydrophilic polymer is defined based on the formula (3).

The volume of the monomer unit in formula (4) is the volume of the optimized structure. The volume of the monomer unit can be calculated, for example, using the Connollysurface method of Materials Studio (registered trademark) manufactured by BIOVIA. At that time, the parameters to be set are as follows.
Grid resolution = Coarse
Grid interval = 0.75 Å
vdW factor = 1.0
Connolly radius=1.0 Å
The hydration energy density of the hydrophilic polymer is 40 to 70 cal·mol ⁻¹ ·Å ⁻³ , preferably 43 to 60 cal·mol ⁻¹ ·Å ⁻³ , more preferably 45 to 55 cal. · mol ^-1 · Å ^-3 . Any preferred lower limit can be combined with any preferred upper limit.

The total number N of monomer species constituting the hydrophilic polymer is not particularly limited as an upper limit, but is preferably 2 to 5, more preferably 2 to 3, and most preferably 2.

Since the hydration energy density of the entire hydrophilic polymer is 40 cal·mol ⁻¹ ·Å ⁻³ or more and 70 cal·mol ⁻¹ ·Å ⁻³ or less, the hydrophilic polymer and the hydrophilic polymer It is considered that the structure of the adsorbed water stabilizes the structure of the impurities in the fermentation liquid and the adsorbed water of the impurities in the fermentation liquid. As a result, the electrostatic interaction or hydrophobic interaction between the hydrophilic polymer present on the hollow fiber membrane surface and the impurities in the fermentation broth is reduced, and the impurities in the fermentation broth adhere to the hollow fiber membrane. is suppressed.

The volume fraction of the monomer units in the above formula (4) and the following formula (5) is the ratio of the number of various monomer units to the total number of monomer units constituting the hydrophilic polymer. As will be described later, it is measured with a nuclear magnetic resonance (NMR) device and calculated from the peak area. If the molar fraction cannot be calculated by NMR measurement for reasons such as overlapping peaks, the molar fraction may be calculated by elemental analysis.

[In Formula (5), N and i are the same as defined above. ]
Hollow fiber membranes are formed by phase separation of hydrophobic polymers and subsequent introduction of hydrophilic polymers, as described later, to form an aggregate of spherical structures composed of hydrophobic polymers and their spherical structures. and a hydrophilic polymer attached to the surface of the structure.

The number average molecular weight of the hydrophilic polymer is preferably 2,000 or more, more preferably 3,000 or more, in order to suppress adhesion of impurities in the fermentation liquid. For high introduction efficiency into the membrane, the number average molecular weight of the hydrophilic polymer is preferably 1,000,000 or less, more preferably 200,000 or less, even more preferably 100,000 or less.

In the hydrophilic polymer, the volume fraction of the monomer unit having the highest hydration energy density calculated based on the formula (4) (referred to as monomer unit j for convenience of explanation) is 35% to 90%. , preferably 40% to 80%, more preferably 40% to 75%, even more preferably 40% to 70%. Any preferred lower limit can be combined with any preferred upper limit.

When the volume fraction is within the above range, the hydrophilic polymer present on the surface of the hollow fiber membrane and the water adsorbed by the hydrophilic polymer are reduced by the effects of both the hydrophilic monomer unit and the hydrophobic monomer unit. It is considered that the interaction between the impurities in the fermentation broth and the impurities in the fermentation broth on the adsorbed water is of an appropriate magnitude, and as a result, the adhesion of the impurities in the fermentation broth is suppressed.

Moreover, in the hydrophilic polymer, the difference in hydration energy density is calculated by the following formula (6).

The difference in hydration energy density is 10 to 100 cal·mol ⁻¹ ·Å ⁻³ , preferably 10 to 80 cal·mol ⁻¹ ·Å ⁻³ , and 10 to 60 cal·mol ⁻¹ ·Å ^{− 3} is more preferred.

When the difference in hydration energy density is within the range, the hydrophilic monomer units of the hydrophilic polymer present on the hollow fiber membrane surface play a role in retaining adsorbed water, and the hydrophobic monomer units control the mobility of adsorbed water. It is thought that it can play the role of As a result, it is considered that the interaction between the hydrophilic polymer present on the material surface and the water adsorbed by the hydrophilic polymer on the impurities in the fermentation broth and the water adsorbed by the impurities in the fermentation broth becomes an appropriate magnitude. As a result, adhesion of impurities in the fermentation broth is suppressed.

The two or more types of monomer units are preferably a hydrophobic monomer unit and a hydrophilic monomer unit.

"Hydrophobic monomer unit" means a monomer unit having a hydration energy density lower than that of a hydrophilic monomer unit, e.g., a monomer selected from the group consisting of vinyl carboxylates, methacrylates, acrylates and styrene derivatives. A repeating unit in a homopolymer or copolymer obtained by polymerizing is preferably used. Of these, homopolymers obtained by polymerizing vinyl carboxylates or copolymers of vinyl carboxylates are preferred because they are easy to balance with hydrophilic monomer units and easy to control the mobility of adsorbed water present on the material surface. A repeating unit in a copolymer obtained by polymerization is more preferred, and a repeating unit in a homopolymer obtained by polymerizing vinyl carboxylate is even more preferred.

"Hydrophilic monomeric unit" means a monomeric unit having a higher hydration energy density than a hydrophobic monomeric unit, for example selected from the group consisting of allylamine, vinylamine, N-vinylamide, N-vinyllactam and N-acryloylmorpholine. Repeating units in homopolymers or copolymers obtained by polymerizing the monomers obtained are preferably used. Of these, the interaction with adsorbed water present on the surface of the material is not too strong, and the balance with the hydrophobic monomer units is easily achieved. A repeating unit in a copolymer obtained by copolymerizing a lactam is preferred, and a repeating unit in a homopolymer obtained by polymerizing an N-vinyllactam is more preferred. Among them, a homopolymer obtained by polymerizing vinylpyrrolidone or a repeating unit in a copolymer obtained by copolymerizing vinylpyrrolidone is more preferred, and a homopolymer obtained by polymerizing vinylpyrrolidone is most preferred. .

Other monomers, for example, monomers containing a reactive group such as a glycidyl group, may be copolymerized to the extent that the actions and functions of the hydrophilic polymer are not impaired.

Examples of the arrangement of hydrophilic monomer units and hydrophobic monomer units in the hydrophilic polymer include graft copolymers, block copolymers, alternating copolymers, and random copolymers. Among these, block copolymers, alternating copolymers, and random copolymers are preferable in that they have a high function of suppressing the adhesion of impurities in the fermentation broth. A random copolymer or an alternating copolymer is more preferable in that it has a good balance. Block copolymers, alternating copolymers, and random copolymers are more likely to contain impurities in the fermentation broth than graft copolymers, such as graft copolymers whose main chain is composed of hydrophilic monomer units and side chains are composed of hydrophobic monomer units. The reason why the adhesion suppression function of is high is that in the graft copolymer, the monomer unit grafted to the main chain has many opportunities to come into contact with proteins, etc., so the characteristics of the graft chain portion are greater than the characteristics of the copolymer. presumably because it affects In addition, alternating copolymers and random copolymers are more preferable than block copolymers in terms of a proper balance between hydrophilicity and hydrophobicity, because in block copolymers, the characteristics of each monomer unit are clearly separated. It is thought that it is for the sake of

The hydrophilic polymer can be synthesized, for example, by a chain polymerization method typified by a radical polymerization method using an azo initiator, but the synthesis method is not limited to this.

The above hydrophilic polymer is produced, for example, by the following production method, but is not limited to this method.

Predetermined amounts of a hydrophilic monomer and a hydrophobic monomer are mixed with a polymerization solvent and a polymerization initiator, and the mixture is stirred for a predetermined time at a predetermined temperature in a nitrogen atmosphere to cause a polymerization reaction. The amount ratio of the hydrophilic monomer and the hydrophobic monomer can be determined according to the molar fraction of hydrophilic monomer units in the copolymer. The reaction solution is cooled to room temperature to terminate the polymerization reaction, and then poured into a solvent such as hexane. A hydrophilic polymer can be obtained by collecting the deposited precipitate and drying it under reduced pressure.

The reaction temperature of the polymerization reaction is preferably 30 to 150°C, more preferably 50 to 100°C, and even more preferably 70 to 80°C.

The pressure for the polymerization reaction is preferably normal pressure.

The reaction time of the polymerization reaction is appropriately selected according to conditions such as the reaction temperature, but is preferably 1 hour or longer, more preferably 3 hours or longer, and even more preferably 5 hours or longer. If the reaction time is short, a large amount of unreacted monomer tends to remain in the copolymer in some cases. On the other hand, the reaction time is preferably 24 hours or less, more preferably 12 hours or less. When the reaction time is long, side reactions such as formation of dimers are likely to occur, and it may become difficult to control the molecular weight.

The polymerization solvent used in the polymerization reaction is not particularly limited as long as it is compatible with the monomer, and examples thereof include ether solvents such as dioxane or tetrahydrofuran, amide solvents such as N,N-dimethylformamide, dimethyl sulfoxide, and the like. sulfoxide solvents, aromatic hydrocarbon solvents such as benzene or toluene, alcoholic solvents such as methanol, ethanol, isopropyl alcohol, amyl alcohol or hexanol, or water, etc. are used, but from the point of toxicity, alcoholic solvents or It is preferred to use water.

As the polymerization initiator for the polymerization reaction, for example, a photopolymerization initiator or a thermal polymerization initiator is used. Although any polymerization initiator that generates radicals, cations or anions may be used, radical polymerization initiators are preferably used because they do not cause decomposition of monomers. Examples of radical polymerization initiators include azo initiators such as azobisisobutyronitrile, azobisdimethylvaleronitrile or azobis(isobutyrate)dimethyl, hydrogen peroxide, benzoyl peroxide, di-tert-butyl peroxide or A peroxide initiator such as dicumyl peroxide is used.

After stopping the polymerization reaction, the solvent into which the polymerization reaction solution is added is not particularly limited as long as it is a solvent that precipitates the copolymer. An ether solvent such as dimethyl ether, ethyl methyl ether, diethyl ether or diphenyl ether is used.

(8) Others When the separation membrane of the present invention takes the form of a hollow fiber membrane, the outer diameter and membrane thickness of the hollow fiber take into consideration the pressure loss in the longitudinal direction inside the hollow fiber membrane within a range that does not impair the strength of the membrane. Then, the membrane module should be determined so that the permeation rate becomes the target value. That is, if the outer diameter is large, it is advantageous in terms of pressure loss, but it is disadvantageous in terms of membrane area because the number of filled tubes is reduced. On the other hand, when the outer diameter is small, the number of fillings can be increased, which is advantageous in terms of membrane area, but disadvantageous in terms of pressure loss. Also, the film thickness is preferably as thin as possible within a range that does not impair the strength. Therefore, as a rough guideline, the outer diameter of the hollow fiber membrane is preferably 0.3 to 3 mm, more preferably 0.4 to 2.5 mm, still more preferably 0.5 to 2.0 mm. . The film thickness is preferably 0.08 to 0.4 times the outer diameter, more preferably 0.1 to 0.35 times, still more preferably 0.12 to 0.3 times.

Preferably, the separation membranes of the present invention are substantially free of macrovoids. Here, macrovoids are pores having a major axis of 50 μm or more observed in the substantial portion of the separation membrane in the cross section of the separation membrane. "Substantially free" means 10 particles/mm ² or less, more preferably 5 particles/mm ² or less in a cross section, and it is most preferable to have no particles at all.

The separation membrane of the present invention has a water permeability at 10 kPa and 25° C. of 0.1 to 10 m ³ /m ² ·h, preferably 0.2 to 5 m ³ /m ² ·h, more preferably 0.4 to 2 m ³ . /m ² ·h, and when the separation membrane of the present invention takes the form of a hollow fiber membrane, the breaking strength of the hollow fiber is 0.3 to 3 kg/membrane, preferably 0.4 to 2.5 kg/membrane. More preferably, the weight is in the range of 0.5 to 2 kg/strand, and the elongation at break is in the range of 20 to 1000%, preferably 40 to 800%, more preferably 60 to 500%. Within this range, sufficient water permeability is exhibited under normal use conditions, and the hollow fiber membrane does not break.

<Separation Membrane Manufacturing Method>
There is no particular limitation on the method for producing the separation membrane according to the present invention. As an example, a method for obtaining a hollow fiber membrane from a polyvinylidene fluoride resin as a hydrophobic polymer will be described below, but the present invention is not limited to these production method examples. An example of the method for producing the hollow fiber membrane described above will be described below. The manufacturing method described below is
(a) step of forming hollow fibers by phase-separating a solution containing a hydrophobic polymer (b) step of heat-treating the hollow fiber membrane (c) introducing a hydrophilic polymer into the heat-treated hollow fibers have a process.

(I) Hollow fiber formation process Examples of methods for producing a hollow fiber membrane from a polyvinylidene fluoride resin include a thermally induced phase separation method, a non-solvent induced phase separation method, a melt extraction method, and a stretching opening method. Of these, it is preferable to use the thermally induced phase separation method or the non-solvent induced phase separation method.

Thermally induced phase separation is phase separation in which a resin solution dissolved at a high temperature is solidified by cooling, and non-solvent induced phase separation is phase separation in which the resin solution is solidified by contact with a non-solvent.

When a hollow fiber membrane is produced using a thermally induced phase separation method, the solvent for the polyvinylidene fluoride resin solution is preferably a poor solvent for the resin, such as cyclohexanone, isophorone, γ-butyrolactone, alkyl ketones such as dimethyl sulfoxide, A poor solvent, such as an ester, in which the resin has a relatively high solubility is particularly preferably employed.

Further, when a hollow fiber membrane is produced using a non-solvent-induced phase separation method, a good solvent for the resin is preferable as the solvent for the polyvinylidene fluoride resin solution, and the good solvent is N-methyl-2-pyrrolidone , dimethylacetamide, dimethylformamide, methyl ethyl ketone, acetone, lower alkyl ketones such as tetrahydrofuran, esters, amides and mixed solvents thereof. On the other hand, the non-solvent is a non-solvent for the resin, water, hexane, pentane, benzene, toluene, methanol, ethanol, carbon tetrachloride, o-dichlorobenzene, trichloroethylene, ethylene glycol, diethylene glycol, triethylene glycol, propylene. Aliphatic hydrocarbons such as glycols, butylene glycols, pentanediol, hexanediol, low molecular weight polyethylene glycols, aromatic hydrocarbons, aliphatic polyhydric alcohols, aromatic polyhydric alcohols, chlorinated hydrocarbons, or other chlorinated Examples include organic liquids and mixed solvents thereof.

heat-treating the separation membrane produced by the thermally induced phase separation method or the non-solvent induced phase separation method at a temperature T that satisfies Tm−70° C.≦T<Tm−40° C., where Tm is the melting point of the separation membrane. is preferably adopted.

Here, the melting point Tm of the separation membrane is the peak top temperature when the temperature of the separation membrane in a dry state is raised at a rate of 10° C./min using a differential scanning calorimetry (DSC measurement) device. It is around 175° C. in the case of hollow fiber membranes.

When the separation membrane is heat-treated at a high temperature close to the melting point of the separation membrane, the micro-Brownian motion of the polymer is activated in the amorphous part in the solid part forming the separation membrane, and then partly crystallizes, or the separation membrane in the solid part forms. The crystal part that melts at a temperature lower than the melting point of is once melted, and then recrystallizes into a crystal part that melts at a higher temperature, causing the solid part to shrink. Since minute voids are present in such crystalline and amorphous portions, shrinkage fills the voids, which is expected to have the effect of reducing adhesion starting points of fouling components such as protein in the fermentation broth. On the other hand, when the melting point of the separation membrane is extremely close to the melting point, the small gaps between the solid portions are clogged due to the shrinkage of the entire membrane during heat treatment. A relatively low heat treatment temperature is preferred. However, since the large voids between the solid portions hardly change during the heat treatment, it is thought that the decrease in the pure water permeation performance is suppressed. Here, the crystal part that melts at a temperature lower than the melting point of the separation membrane means the following crystal part. When the dried separation membrane is heated at a rate of 10° C./min using a DSC measuring device, a broad endothermic peak appears. Among the endothermic peaks, the crystal part resulting from the portion tailing to the lower temperature side than the peak top corresponding to the melting point of the separation membrane is the crystal part that melts at a temperature lower than the melting point of the separation membrane. That is, it is considered to be the energetically unstable crystal part among the entire crystal parts.

In this way, in the thermally induced phase separation method and the non-solvent induced phase separation method, by using a good solvent or a poor solvent in which the resin has a high solubility, the resin and the solvent can be mixed at the molecular level, so when solidified, Solvent molecules intervene between the resin molecules. As a result, it is believed that the number of intermolecular voids increases, and that crystal parts that melt at a temperature lower than the melting point of the separation membrane, ie, energetically unstable crystal parts, increase. When the separation membrane of the present invention has the shape of a hollow fiber membrane, heat treatment of the hollow fiber membrane in such a state is thought to improve the effect of reducing the starting points of adhesion of fouling components.

There are mainly two types of phase separation mechanisms in the thermally induced phase separation method. One is a liquid-liquid phase separation method in which a resin solution that is uniformly dissolved at high temperature separates into a dense phase and a dilute phase due to the decrease in dissolving ability of the solution when the temperature is lowered, and the other is a resin that is uniformly dissolved at high temperature. It is a solid-liquid phase separation method in which the solution undergoes phase separation into a polymer solid phase and a polymer dilute solution phase due to crystallization of the resin when the temperature is lowered. The former method mainly forms a three-dimensional network structure, and the latter method forms a spherical structure. In the present invention, for the reasons described above, it is more preferable to form a spherical structure by the latter phase separation mechanism. In the case of the spherical structure, since the solid portion is bulky, the voids between the solid portions are less likely to shrink, and this is also the reason why it is preferable to maintain high pure water permeation performance. For this reason, it is preferable to select a resin concentration and a solvent that induce solid-liquid phase separation. When cooling, it is preferable to use a cooling bath, and it is preferable to use the same solvent as the resin solution or to contain a non-solvent for the resin at a low concentration in order to speed up the solidification.

In contrast to the thermally induced phase separation method and the non-solvent induced phase separation method, the melt extraction method kneads a resin, inorganic fine particles, and an organic liquid with low solubility in the resin at a high temperature to form a high-temperature liquid, which is then solidified. , and then extracting the inorganic fine particles and the organic liquid to form voids between the solid portions where the molecules are gathered. In this method, since the resin and the organic liquid are not mixed at the molecular level in the high-temperature liquid, solvent molecules do not intervene between the resin molecules when solidified. Also, the kneading temperature is higher than the melting point of the resin. For this reason, even if the hollow fiber membrane is heat-treated at a temperature lower than the melting point after solidification, the crystalline state does not change and no improvement in the effect of reducing the fouling starting points is observed.

Further, the stretch opening method is a method in which a resin is melted, shaped, annealed, and stretched. Like the melt extraction method, this method does not use a solvent and melts, but after solidification, it is stretched at a very high magnification of 3 times or more to change the crystal state. However, this change promotes crystallization, and subsequent heat treatment at a temperature below the melting point improves the dimensional stability at temperatures below the heat treatment temperature, but the crystalline state hardly changes, reducing the starting points for adhesion of fouling components. No improvement in efficacy was observed.

For the above reasons, it is necessary to use the thermally induced phase separation method or the non-solvent induced phase separation method as the method for producing the separation membrane of the present invention. - A liquid phase separation method is more preferably employed.

In the solid-liquid phase separation method of the thermally induced phase separation method, the resin solution is separated as a method of changing the size of the spherical structure and the size of the pores between the spherical structures asymmetrically with respect to the thickness direction of the separation membrane. There is a method of imparting a temperature gradient to the resin solution in the thickness direction of the separation membrane between the step of forming into a membrane shape and the step of solidifying the resin solution by solid-liquid thermally induced phase separation in a cooling bath.

“Provide a temperature gradient” means that the temperature of a part of the resin solution formed in the film shape differs from the temperature of the other part in the thickness direction. More specifically, "providing a temperature gradient" refers to increasing the temperature from one surface to the other surface of the resin solution formed in the form of a separation membrane.
As a specific method for applying a temperature gradient, when manufacturing a hollow fiber membrane, (1) the temperature of the die is set higher than the temperature of the resin solution supplied, and (2) the flow of the fluid passing through the inner nozzle of the die is At least one of (3) heating the resin solution idling between the nozzle and the cooling bath is performed.

By carrying out at least one of (1) and (3) above, the outer spherical structure of the hollow fiber membrane can be made relatively large. Moreover, by performing the above (2), the outer spherical structure of the hollow fiber membrane can be made relatively small. In order to carry out the above (3), a heating device such as a heater may be arranged between the nozzle 1 and the cooling bath, or a device for spraying or applying a high-temperature solvent may be arranged. .
In addition, as a specific method for "providing a temperature gradient", when manufacturing a flat film, (2′) heating one side of the flat-film-like resin solution running idle between the mouthpiece 2, which is a slit die, and the cooling bath; performing at least one of To execute (2′), a method similar to (3) above can be adopted.

By "providing a temperature gradient", it is preferable to make the temperature of the portion to be a spherical structure having a large average diameter relatively higher than the temperature of the portion to be a spherical structure having a small average diameter. In other words, if it is desired to increase the average diameter of the spherical structure on the surface layer of the surface of the membrane that contacts the liquid to be treated and to decrease the average diameter on the inside of the membrane, the temperature of the surface layer should be relatively higher than the temperature of the inside. preferably.

In the method of increasing the temperature relatively, it is possible to lower the resin temperature in areas other than the portion where the spherical structure having a large average diameter is desired. The effect is small compared to the effect of increasing the resin temperature and enlarging the spherical structure. This is because the formation of primary nuclei progresses gradually in the metastable region between the melting temperature and the crystallization temperature of the resin solution.

For example, when a temperature gradient is imparted to the resin solution in a relatively short period of time by cooling to a specific temperature, the conditions are insufficient for the progress of primary nucleus formation. On the other hand, the primary nuclei after formation are relatively greatly affected by the temperature rise of the resin solution and decrease, resulting in a decrease in the number of spherical structures after solidification.

That is, the primary nucleus of the resin solution behaves differently with respect to temperature changes during temperature rise and temperature fall. Therefore, when changing the spherical structure diameter by "providing a temperature gradient", a step of partially heating the resin solution is preferably used.

In this step, the temperature on the high temperature side of the temperature gradient may be set to a temperature at which the number of primary nuclei of crystals is reduced more than that in other portions of the resin solution.
By setting the temperature of a part of the resin solution to a temperature at which the number of primary crystal nuclei decreases more than the temperature of the other part of the resin solution and causing solid-liquid phase separation, a spherical structure having a large diameter can be formed in that part. .

In the step of applying the temperature gradient, the average temperature increase rate when applying the temperature gradient, that is, the average rate of temperature change of the resin solution (temperature temperature increase rate) is set to 30 ° C./min or more and 700 ° C./min or less, and the application time is (Heating time) is preferably 0.1 seconds or more and 5.0 seconds or less. Heating at an average temperature increase rate of 75° C./min or more and 700° C./min or less is more preferably 0.2 seconds or more and 2.0 seconds or less, and more preferably 0.2 seconds or more and 1.0 seconds or less.

When the average heating rate of temperature change is 30° C./min or more, the spherical structure on the surface of the separation membrane can be enlarged, and high water permeability can be achieved. When the rate of temperature change is 700° C./min or less, it is possible to selectively enlarge only the spherical structure on the surface of the separation membrane, so that high strength and elongation can be maintained. By applying such a temperature change to the resin solution to provide a temperature gradient, the partial number of primary nuclei in the resin solution can be controlled.

Further, when the heating time is 0.1 second or more, the spherical structure on the surface of the separation membrane can be enlarged, and high water permeability can be achieved. On the other hand, if the heating time is 5.0 seconds or less, only the spherical structure on the surface of the separation membrane can be selectively enlarged, so that the reduction in strength and elongation can be maintained at a high level. Hereinafter, for convenience of explanation, the terms "heating time" and "average heating rate" will be used.

The average temperature increase rate is obtained by measuring the resin solution temperature, that is, the primary crystal nucleus formation temperature T _n immediately before the step of solidifying the resin solution by solid-liquid thermally induced phase separation in a cooling bath, by thermography or the like, and comparing T _n with heating. It can be calculated as shown in Equation (7) from the relationship of time _th .

When a die for hollow fiber membranes and a die for flat membranes are used, when the die for discharging the resin solution is heated to impart a temperature gradient to the resin solution, the heating time is such that the resin solution passes through the die. is the time it takes to

In addition, the cooling bath temperature T _s is set to (T _c −T _s )/(T _n −T _s )<0.50 with respect to the crystallization temperature T _c , that is, the temperature at which crystals grow by homogeneous nucleation. is preferred. T _n −T _s is a parameter that becomes the overall cooling rate, while T _c −T _s is a parameter that contributes to crystal growth. It was found that by reducing the temperature difference that contributes to crystal growth in the overall cooling rate, crystal growth starting from the primary nuclei proceeds, and a spherical structure distribution can be developed in accordance with the distribution of the primary nuclei due to the temperature gradient. . More preferably, (T _c −T _s )/(T _n −T _s )<0.45, and still more preferably (T _c −T _s )/(T _n −T _s )<0.40.

In the separation membrane manufacturing method of the present invention, it is preferable to satisfy the relationship 15<T _n −T _s <35. When T _c −T _s is greater than 15° C., it is possible to suppress the solidification time from becoming too long, and to prevent the manufacturing equipment from becoming excessively large. Further, the inventors have found that when T _c −T _s is less than 35° C., the growth progresses starting from the primary nuclei described above.

Also, T _n -T _s is preferably less than 100°C, more preferably less than 80°C. By adopting such an operation, a wider gradient can be applied in the film thickness direction.

Here, when the separation membrane of the present invention takes the shape of a hollow fiber membrane, the hollow fiber membrane produced by using a non-solvent induced phase separation method or a thermally induced phase separation method expands the pores before the heat treatment and is pure. Stretching is also preferably employed in order to improve water permeability. The stretching conditions are preferably a temperature range of 50 to 120° C., more preferably 60 to 100° C., and a draw ratio of 1.1 to 4 times. If the temperature is less than 50°C, it is difficult to stably and uniformly draw the membrane, and if the temperature exceeds 120°C, the hollow fiber membrane may soften and the hollow portion may collapse. Further, the stretching is preferably carried out in a liquid because temperature control is easy, but it may be carried out in a gas such as steam. As the liquid, water is preferable because it is simple, but when stretching is performed at about 90° C. or higher, it is also preferable to use low-molecular-weight polyethylene glycol or the like.

(II) Heat Treatment Process The separation membrane to be heat treated is preferably in a dry state or in a wet state with a non-solvent for the resin so as not to be dissolved by heating. In particular, when the resin component is a fluorine-based resin or a sulfone-based resin, it is preferably moistened with water vapor in order to prevent the surface of the separation membrane from being extremely wetted with water.

In addition, in order to effectively suppress the effect of clogging the minute gaps between the solid parts and making the branching of the flow paths poor, water-soluble compounds were applied to the minute gaps between the solid parts and then the water vapor was applied. It is highly preferred to carry out the heat treatment under moist conditions. When a water-soluble compound is heat-treated in a state in which it enters the voids between the solid parts, the compound prevents pore clogging, while the compound becomes fluid due to water vapor, which inhibits structural changes in the separation membrane. not be considered. At this time, it is considered that minute voids in the solid portion to which the compound is not applied are clogged. Among water-soluble compounds, it is generally known that water-soluble moisturizing agents inhibit pore clogging when applied to separation membranes during dry storage. It is economical to apply a water-soluble moisturizing agent because it can be done without using. Water-soluble moisturizing agents include glycols such as glycerin and propylene glycol.
Heat treatment of separation membranes is generally known, but in the prior art, it is used for dimensional stability at temperatures below the heat treatment temperature. Therefore, the heat treatment temperature is lower than that of the present invention, and the separation membrane does not have excellent filtration performance for the fermented liquid.

(III) Step of Introducing Hydrophilic Polymer The type of hydrophilic polymer is as described in the section on the separation membrane. As a method for introducing a hydrophilic polymer, an aqueous solution in which the hydrophilic polymer is dissolved is passed through or immersed in the hollow fiber membrane, followed by irradiation or heat treatment to insolubilize the hydrophilic polymer. A method of forming a covalent bond through a chemical reaction with an existing reactive group can be mentioned.
As a method for changing the introduction amount of hydrophilic polymer asymmetrically with respect to the thickness direction of the separation membrane, an aqueous solution in which the hydrophilic polymer is dissolved is passed from one membrane surface of the hollow fiber membrane to the other membrane surface. However, by performing radiation irradiation or heat treatment, the hydrophilic polymer is consumed while passing the liquid, and a method of setting the concentration of the hydrophilic polymer in the aqueous solution that is in contact with each thickness region to be different.

If the concentration of the hydrophilic polymer aqueous solution is too low, a sufficient amount of the hydrophilic polymer cannot be introduced onto the surface. Therefore, the copolymer concentration in the aqueous solution is preferably 10 ppm or more, more preferably 100 ppm or more, and most preferably 500 ppm or more. However, if the concentration of the hydrophilic polymer in the aqueous solution is too high, there is a concern that elution from the module may increase. preferable. The number average molecular weight of the hydrophilic polymer is measured by gel permeation chromatography (GPC).

In addition, when the hydrophilic polymer is poorly soluble or insoluble in water, it is hydrophilic in an organic solvent that does not dissolve the hollow fibers or a mixed solvent of water and an organic solvent that is compatible with water and does not dissolve the hollow fibers. Polymers may be dissolved. Specific examples of the organic solvent that can be used in the organic solvent or the mixed solvent include, but are not limited to, alcoholic solvents such as methanol, ethanol, and propanol.

Moreover, when the ratio of the organic solvent in the mixed solvent increases, the hollow fibers may swell and the pore diameter of the hollow fiber membrane may change. Therefore, the weight fraction of the organic solvent in the mixed solvent is preferably 60% or less, more preferably 10% or less, and most preferably 1% or less.

α-rays, β-rays, γ-rays, X-rays, ultraviolet rays, electron beams, or the like can be used for the radiation irradiation. Here, radiation methods using γ-rays or electron beams are preferable from the viewpoint of safety and simplicity. The irradiation dose of radiation is preferably 15 kGy or more, more preferably 25 kGy or more. A hydrophilic polymer can be effectively introduced by setting the dose to 15 kGy or more. Moreover, the irradiation dose is preferably 100 kGy or less. This is because if the irradiation dose exceeds 100 kGy, the copolymer tends to undergo three-dimensional cross-linking, decomposition of the ester group portion of the vinyl carboxylate monomer unit, and the like.

An antioxidant may be used to suppress the cross-linking reaction during irradiation. An antioxidant means a substance that has the property of easily donating electrons to other molecules. Examples include water-soluble vitamins such as vitamin C, polyphenols, and alcoholic solvents such as methanol, ethanol, and propanol. but not limited to these. These antioxidants may be used alone or in combination of two or more. When an antioxidant is used, it is necessary to consider safety, so low-toxic antioxidants such as ethanol and propanol are preferably used.

In addition, as a method of forming a covalent bond by a chemical reaction with a reactive group, specifically, a reactive group such as an amino group, a sulfonic acid group, and a halogenated alkyl group on the surface of the material base material, and a copolymer is achieved by reacting with a reactive group introduced into the end of the main chain or side chain of the

Methods for introducing reactive groups onto the material surface include, for example, a method of polymerizing a monomer having a reactive group to obtain a base material having a reactive group on the surface, and a method of reacting with ozone treatment or plasma treatment after polymerization. a method of introducing a sexual group, and the like.

Examples of methods for introducing a reactive group to the end of the main chain of the copolymer include 2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propionamide] and 4,4′- Examples include a method using an initiator having a reactive group such as azobis(4-cyanovaleric acid).

As a method for introducing a reactive group into the side chain of the copolymer, a method of copolymerizing a monomer having a reactive group such as glycidyl methacrylate to the extent that the action/function of the copolymer is not hindered. is mentioned.

The introduction amount of the hydrophilic polymer into the hollow fiber membrane can be quantified by total reflection infrared spectroscopy (ATR-IR), as described above. Also, if necessary, it can be quantified by NMR measurement, X-ray electron spectroscopy (XPS), or the like.

<Use of separation membrane module>
The separation membrane of the present invention can be used for liquid filtration. Fermented liquid is preferable as the undiluted liquid to be filtered. The fermented liquid is not particularly limited in terms of the type of microorganism or the fermentation product, but examples include beer, wine, vinegar, soy sauce, amino acid fermented liquid, organic acid fermented liquid, biopharmaceutical fermented liquid, etc. The fermented liquid can be filtered by filtration. Unnecessary components in the product such as turbidity can be removed. The hollow fiber membrane module described above is suitable for these applications because clogging during filtration is unlikely to occur and performance recoverability by chemical cleaning after clogging is maintained over a long period of time.

When using the separation membrane, it is preferable to orient the first surface toward the undiluted solution. That is, it is preferable to supply the undiluted liquid to the first surface and take out the permeated liquid from the second surface.

A hollow fiber membrane can be used as a hollow fiber membrane module. A module is a bundle of multiple hollow fiber membranes that is housed in a cylindrical container and fixed at one or both ends with polyurethane or epoxy resin to collect permeated water. It means that the both ends of the pipe are fixed so that the permeated water can be collected. By providing pressurizing means such as a pump or water level difference on the undiluted solution side of the hollow fiber membrane module, or by providing suction means such as a pump or siphon on the permeated liquid side, membrane filtration of the fermented liquid, which is the undiluted liquid, is performed. It can be used as a separation device. Using this separation device, a purified permeate can be produced from the fermentation broth.

The present invention is not limited to the above-described embodiments, and can be modified as appropriate. In addition, the material, shape, size, numerical value, form, number, location, etc. of each component in the above-described embodiment are arbitrary and not limited as long as the present invention can be achieved.

EXAMPLES The present invention will be described in more detail with reference to Examples below, but the present invention is not limited to these Examples. In the following examples, the case where the separation membrane of the present invention takes the shape of a hollow fiber membrane will be described.

<Measurement of crystallization temperature Tc of polyvinylidene fluoride resin solution>
Using a high-sensitivity differential scanning calorimeter (DSC6200 manufactured by Seiko Instruments Inc.), a mixture having the same composition as the film-forming polymer stock solution composition such as polyvinylidene fluoride resin and solvent was sealed in a sealed DSC container, and the temperature was increased at a rate of 10 ° C. /min to the dissolution temperature and held for 30 minutes to dissolve uniformly. After that, the rise temperature of the crystallization peak observed in the process of lowering the temperature at a temperature lowering rate of 10° C./min was defined as the crystallization temperature Tc.

<Measurement of pore size distribution of hollow fiber membrane by mercury porosimetry>
The hollow fiber membrane was absolutely dried by the following method. The hollow fiber membrane which was not heat-treated and was wet with water was freeze-dried at −20° C. for about 50 hours and then vacuum-dried at room temperature for about 8 hours. The heat-treated hollow fiber membrane was vacuum-dried at room temperature for about 8 hours. This absolute dry hollow fiber membrane was cut to a length of about 5 mm, and the weight of the sample was measured with an electronic balance (AW220 manufactured by Shimadzu Corporation). The pore size distribution was measured with a Pore Sizer 9320 manufactured by Micromeritex. After the test piece was enclosed in a glass cell of about 5 cm ³ attached to the device and mercury was injected under reduced pressure, it was placed in a pressure vessel attached to the device via oil at about 4 kPa to 207 MPa (corresponding to a pore diameter of about 7 nm to 350 μm). ) was performed by increasing the pressure in the range of . The surface tension of mercury was calculated using 484 dyn/cm and the contact angle of mercury was 141.3°.

<Preparation of thin film section, measurement of specific gravity>
Cut out the hollow fiber membrane moistened with water to a film length of 10 cm, cut it with a razor blade so that the cross section becomes a semicircle, and cut it into two razor blades (width 4 cm) arranged at intervals of 0.5 mm. The cylindrical film was pressed so that the center line of the film came into contact with the film, and the portion (film length: 4 cm) in contact with the single-edged razor was divided into three parts. A long section (4 cm x 0.5 mm) of the central portion of the three-divided membrane was collected. 20 long sections obtained by repeating the same operation were air-dried at 25 ° C. for 1 hour, covered with OCT compound (manufactured by Tissue Tek), allowed to penetrate to the inside of the membrane, and then placed in a cryomold. Twenty long pieces were arranged so that the inner surface side of the tube was the bottom surface to form a bundle of pieces (4 cm×10 mm). After rapid freezing in a cryomold at −20° C., a cryostat (Leica Jung CM3000) was used to slice the section bundle into 5 μm increments perpendicular to the film thickness direction. A region corresponding to the inner surface was collected from the surface to obtain a thin film slice in which the region name was assigned in order from S1 from the outer surface side.

Subtract the dry thin-film section weight (g) from the wet thin-film section weight (g) and divide by the specific gravity of water (1.00 g/cm ³ ) to obtain the void volume (cm ³ ), and the dry thin-film section weight (g ) is divided by the specific gravity of the hollow fiber membrane component (for example, 1.78 g/cm ³ for a vinylidene fluoride homopolymer) to determine the polymer volume (cm ³ ). ³ ) and the sum of the polymer volume (cm ³ ) is taken as the thin film section specific gravity (g/cm ³ ) including voids.

<Evaluation of Melting Point Temperature and Heat of Fusion of Adsorbed Water on Channel Wall>
The melting point temperature and the heat of fusion of the adsorbed water on the channel wall were measured using a high-sensitivity differential scanning calorimeter (DSC6200 manufactured by Seiko Instruments Inc.), and the thin film section wetted with water was measured at 25 ° C. for 1 hour. Then, about 3 mg was weighed with an electronic balance (AW220 manufactured by Shimadzu Corporation) and measured under a nitrogen atmosphere. From the area value of the endothermic peak (melting peak) due to the melting of the intermediate water represented by formula (1) having a peak top at -15.0 to -0.1 ° C., the heat of fusion (J/cm ³ ) is calculated. Calculated. The volume value of the measurement sample used to calculate the heat of fusion is calculated from the weight (g) of the thin film section sample when wet, and endothermic heat absorption by evaporation of water (including all free water, intermediate water, and non-freezing water) at around 100 ° C. A value obtained by subtracting the water content (g) calculated from the peak area value and dividing by the thin film section specific gravity (g/cm ³ ) including the void portion is used.

A ratio Q _max /Q _min of the heat of fusion per volume in the region Sq _max where the heat of fusion Q per volume of intermediate water is the maximum and the region Sq _min where the heat of fusion Q is the minimum was calculated.

<Measurement of average pore diameter and pore specific surface area of hollow fiber membrane by gas adsorption method>
The thin film slice was dried under reduced pressure, and the weight of the sample was measured with an electronic balance (AW220 manufactured by Shimadzu Corporation). The nitrogen gas adsorption amount was measured using an automatic specific surface area/pore size distribution measuring device (BELSORP-mini II manufactured by Microtrac Bell). The average pore diameter and BET specific surface area were calculated using the attached analysis program.

<Measurement of content of hydrophilic polymer>
A 2 cm hollow fiber membrane was dissolved in 1 mL of dimethyl sulfoxide and measured by ¹ H-NMR using JNM-ECZ400R manufactured by JEOL. This measurement was performed at two arbitrary points on the hollow fiber membrane, and the amount of the hydrophilic polymer was determined when the ratio of PVDF detected was taken as 100.

<Depth direction distribution of hydrophilic polymer>
After washing the hollow fiber membrane with distilled water, the surface was exposed with a single blade. After cleaning by Ar gas cluster ion beam (Ar-GCIB) etching, TOF-SIMS measurement was performed using TOF.SIMS 5 manufactured by ION-TOF. The primary ion was Bi3++, and the secondary ion polarities were positive and negative. In order to correct the intensity distribution due to the tilt of the sample, the intensity distribution derived from the hydrophilic polymer is taken relative to all ions detected for each pixel, and the content of the hydrophilic polymer in the film thickness direction is calculated. asked for quantity.

<Fabrication of membrane module>
A plurality of hollow fiber membranes were cut into lengths of about 30 cm and wound with a polyethylene film to form a hollow fiber membrane bundle. This hollow fiber membrane bundle was inserted into a cylindrical module case made of polycarbonate, and both ends were fixed with an epoxy potting agent. The ends were cut to obtain modules open at both ends. The number of hollow fiber membranes was appropriately set so that the membrane area based on the inner diameter of the hollow fiber membranes was 100 to 200 cm ² . The cylindrical module case is provided with two ports near both ends so that the outer surface of the hollow fiber membrane can be perfused with fluid. The hollow part of the fiber membrane was allowed to be perfused with fluid.

<Polysaccharide occlusion test>
A 5.0% by weight ethanol aqueous solution containing 2.0% by weight of water-soluble polysaccharide β-glucan (manufactured by Megazyme) was prepared. Tannin (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added in an amount of 0.05% by weight so that the average dispersion diameter was 100 nm or more and less than 1000 nm. Filtration is performed at a constant flow rate through the separation membrane module at 2.0 m ³ /m ² /day, and the filtration is stopped when the transmembrane pressure difference becomes 10 times the initial transmembrane pressure difference. About 1.0 L/m ² of pure water was passed through to obtain a clogging membrane.

<Measurement of β-glucan>
β-glucan was measured using a β-glucan assay kit Mixed-linkage beta-glucan manufactured by Megazyme. Measurements were performed according to the attached protocol.

<Measurement of average dispersion diameter>
The average dispersion diameter of the aqueous solution used in the polysaccharide occlusion test was measured using an electrophoretic light scattering device (ELS-8000 manufactured by Otsuka Electronics Co., Ltd.). Analysis of the average dispersion diameter was calculated by the cumulant method using analysis software attached to the device.

<Evaluation of polysaccharide component ratio in occluded membrane by TOF-SIMS measurement>
The occlusion membrane obtained by the polysaccharide occlusion test was cut into a length of 1 cm using a single-edged razor, and the cross section was cleaned by argon gas cluster ion beam etching.

A polysaccharide component-derived peak normalized by a characteristic peak of a membrane base material (for example, a C ₃ HF ₄ ⁺ peak in the case of a polyvinylidene fluoride membrane) from the measured mass spectrum obtained by measuring a cross section of the membrane by TOF-SIMS. (eg, C ₃ H ₅ O ₃ ^-peak ) was calculated, and a line profile with a width of 80 μm in the film thickness direction was drawn.

Assuming that the outer surface side rising position of the peak intensity derived from the membrane base material is 0, the line profile was divided every 5 μm in the thickness direction, and region names were assigned in order from S1 from the outer surface side. The average value of the polysaccharide component peak values in each region was taken as the amount of polysaccharide components present in the polysaccharide-occluded state.

A logarithmic value Log(P _max /P _min ) of the abundance ratio in the region Sp _max with the largest abundance and the region Sp _min with the smallest abundance was calculated.

<Water permeability evaluation of separation membrane>
A small module with a length of about 10 cm consisting of about 1 to 10 hollow fiber membranes is produced, and distilled water is sent from the first surface under the conditions of a temperature of 25 ° C. and a filtration differential pressure of 18.6 kPa, and the entire amount is filtered. The value obtained by measuring the amount of permeated water (m ³ ) for a certain period of time was converted into a unit time (hr), a unit effective membrane area (m ² ), and calculated per 50 kPa.

<Evaluation of actual liquid operation>
Commercially available unfiltered beer "Ginga Kogen Beer" containing brewer's yeast (hereinafter referred to as evaluation beer) was used. 2 L of beer for evaluation maintained at 0 ° C. was prepared in a container, and the beer for evaluation perfused the outer surface of the hollow fiber membrane from this container via a pump and returned to the container, and at the same time, the filtrate filtered by the hollow fiber membrane. A circuit was set up to collect in a container different from the container containing the beer for evaluation. At that time, it was made possible to measure the inlet pressure and outlet pressure of the beer for evaluation to the module and the pressure on the filtration side. Beer for evaluation was introduced so that the film surface linear velocity was 1.5 m/sec. In addition, the filtration speed was adjusted to 1 m/d, and the operation was performed at a constant flow rate. In this state, the outer surface of the hollow fiber membrane was perfused with beer for evaluation at 5±3° C., and cross-flow filtration was continuously performed by filtering a portion of the beer. As the operation continues, the hollow fiber membrane clogs and the water permeability decreases, but the transmembrane pressure difference (TMP) increases because of the constant flow rate filtration. TMP is calculated from the following formula. where Pi is the inlet pressure, Po is the outlet pressure and Pf is the filtration side pressure.
TMP=((Pi+Po)/2)-Pf.
The time [h] for the TMP to rise to 150 kPa was measured, and the amount of beer processed was calculated from the following formula. If high water permeability can be maintained for a long time, the amount of beer processed will be large. If the permeability decreases faster, the beer throughput will be lower.
Amount of beer processed [L/m 2 ]=filtration rate 100 [L/m ² /h]×time for increasing pressure to 150 kPa [h].

<Inhibitory evaluation>
Regarding the beer for evaluation, the liquid to be filtered and the filtrate are allowed to stand at room temperature for 30 minutes after sampling, and the turbidity is measured with a nephelometric turbidity meter. After that, the blocking rate was calculated from the following formula.

Rejection rate (%) = (Undiluted solution turbidity - Filtrate turbidity) / Undiluted solution turbidity <Flavor evaluation>
The filtrate obtained by the actual liquid operation evaluation was subjected to a sensory test, and 10 panelists performed a 5-grade evaluation. The average score of 10 people was used as the flavor evaluation score.

[Example 1]
38% by weight of a vinylidene fluoride homopolymer having a weight average molecular weight of 417,000 and 62% by weight of gamma-butyrolactone were dissolved at 150°C. This resin solution was held at 100°C in the range of (Tc + 20)°C to (Tc + 55)°C for 20 seconds under a pressure of 1.2 MPa, and then the outer tube was heated to 108°C. The liquid was sent to the type mouthpiece. The resin solution was discharged 4.7 seconds after entering the double-tube spinneret. While the resin solution was passed through the outer tube of the spinneret, a 90% by weight aqueous solution of γ-butyrolactone at 100° C. was simultaneously discharged from the inner tube of the double-tube spinneret. The discharged resin solution was solidified for 1 minute in a bath containing an aqueous solution of 90% by weight of γ-butyrolactone at a temperature of 25°C. After solidification, the resulting film was washed with water and stretched 1.5 times in hot water at 95°C. The stretched hollow fiber membrane was washed with water, immersed in 30% glycerin for 2 hours, and air-dried overnight. After that, heat treatment was performed under steam at 125° C. for 1 hour.

The membrane performance, polysaccharide clogging state, and intermediate water distribution of the obtained hollow fiber membrane were as shown in Table 1, and the average score of flavor evaluation was 4.2.

[Example 2]
38% by weight of a vinylidene fluoride homopolymer having a weight average molecular weight of 417,000 and 62% by weight of gamma-butyrolactone were dissolved at 150°C. This resin solution was held at 100°C in the range of (Tc + 20)°C to (Tc + 55)°C for 20 seconds under a pressure of 1.2 MPa, and then sent to a pipe whose outside was heated to 125°C. After that, the liquid was sent to a double tube type mouthpiece heated to 100°C. 5.4 seconds after entering the piping heated to 125° C., the liquid was sent to the double-pipe mouthpiece. While the resin solution was passed through the outer tube of the spinneret, a 90% by weight aqueous solution of γ-butyrolactone at 100° C. was simultaneously discharged from the inner tube of the double-tube spinneret. The discharged resin solution was solidified for 1 minute in a bath containing an aqueous solution of 90% by weight of γ-butyrolactone at a temperature of 25°C. After solidification, the resulting film was washed with water and stretched 1.5 times in hot water at 95°C. The stretched hollow fiber membrane was washed with water, immersed in 30% glycerin for 2 hours, and air-dried overnight. After that, heat treatment was performed under steam at 125° C. for 1 hour.

The membrane performance, polysaccharide clogging state, and intermediate water distribution of the obtained hollow fiber membrane were as shown in Table 1, and the average score of flavor evaluation was 4.6.

[Example 3]
36% by weight of a vinylidene fluoride homopolymer having a weight average molecular weight of 417,000 and 64% by weight of gamma-butyrolactone were dissolved at 150°C. This resin solution was held at 99°C in the range of (Tc + 20)°C to (Tc + 55)°C for 20 seconds under a pressure of 1.2 MPa, and then the outer tube was heated to 108°C. The liquid was sent to the type mouthpiece. The resin solution was discharged 5.2 seconds after entering the double-tube spinneret. While the resin solution was passed through the outer tube of the spinneret, a 90% by weight aqueous solution of γ-butyrolactone at 100° C. was simultaneously discharged from the inner tube of the double-tube spinneret. The discharged resin solution was solidified for 1 minute in a bath containing an aqueous solution of 90% by weight of γ-butyrolactone at a temperature of 25°C. After solidification, the resulting film was washed with water and stretched 1.5 times in hot water at 95°C. The stretched hollow fiber membrane was washed with water, immersed in 30% glycerin for 2 hours, and air-dried overnight. After that, heat treatment was performed under steam at 125° C. for 1 hour.
The membrane performance, polysaccharide clogging state, and intermediate water distribution of the obtained hollow fiber membrane were as shown in Table 1, and the average score of flavor evaluation was 4.2.

[Example 4]
36% by weight of a vinylidene fluoride homopolymer having a weight average molecular weight of 417,000 and 64% by weight of dimethyl sulfoxide were dissolved at 120°C. After holding this resin solution at 75°C in the range of (Tc + 20)°C to (Tc + 55)°C for 20 seconds under a pressure of 1.2 MPa, the outer tube was heated to 83°C. The liquid was sent to the type mouthpiece. The resin solution was discharged 4.8 seconds after entering the double-tube spinneret. While the resin solution was passed through the outer tube of the spinneret, a 90% by weight aqueous solution of dimethylsulfoxide at 75° C. was discharged from the inner tube of the double-tube spinneret at the same time. The extruded resin solution was solidified for 1 minute in a bath of 90% by weight of dimethyl sulfoxide in an aqueous solution at a temperature of 18°C. After solidification, the resulting film was washed with water and stretched 1.5 times in hot water at 95°C. The stretched hollow fiber membrane was washed with water, immersed in 30% glycerin for 2 hours, and air-dried overnight. After that, heat treatment was performed under steam at 125° C. for 1 hour.

The membrane performance, polysaccharide clogging state, and intermediate water distribution of the obtained hollow fiber membrane were as shown in Table 1, and the average score of flavor evaluation was 4.3.

[Example 5]
38% by weight of a vinylidene fluoride homopolymer having a weight average molecular weight of 417,000 and 62% by weight of gamma-butyrolactone were dissolved at 150°C. This resin solution was held at 98°C in the range of (Tc + 20)°C to (Tc + 55)°C for 20 seconds under a pressure of 1.2 MPa, and then sent to a pipe whose outside was heated to 132°C. After that, the liquid was sent to a double tube type mouthpiece heated to 100°C. 5.4 seconds after entering the piping heated to 132° C., the liquid was sent to the double-pipe mouthpiece. While the resin solution was passed through the outer tube of the spinneret, a 90% by weight aqueous solution of γ-butyrolactone at 100° C. was simultaneously discharged from the inner tube of the double-tube spinneret. The discharged resin solution was solidified for 1 minute in a bath containing an aqueous solution of 90% by weight of γ-butyrolactone at a temperature of 25°C. After solidification, the resulting film was washed with water and stretched 1.5 times in hot water at 95°C. The stretched hollow fiber membrane was washed with water, immersed in 30% glycerin for 2 hours, and air-dried overnight. After that, heat treatment was performed under steam at 125° C. for 1 hour.

The membrane performance, polysaccharide clogging state, and intermediate water distribution of the obtained hollow fiber membrane were as shown in Table 1, and the average score of flavor evaluation was 4.1.

[Example 6]
A hollow fiber membrane was obtained in the same manner as described in Example 1, except that the temperature of the outer tube of the double tube spinneret was set to 100°C, and one end of the fiber was sealed by thermocompression bonding. At the other end, an epoxy potting agent was used to bond the hollow portion and the syringe needle. Vinylpyrrolidone/vinyl acetate random copolymer (Kollidon VA64; manufactured by BASF). After immersing the prepared hollow fiber membrane in a 0.1% by weight ethanol aqueous solution in which 1000 ppm of a hydrophilic polymer is dissolved, the syringe is used. The aqueous solution was permeated into the membrane while removing the air from the hollow portion. The hollow fiber membrane was taken out from the aqueous solution, drained, and irradiated with 25 kGy of γ-rays to introduce a vinylpyrrolidone/vinyl acetate random copolymer into the hollow fiber membrane.

The membrane performance, polysaccharide clogging state, and intermediate water distribution of the obtained hollow fiber membrane were as shown in Table 1, and the average score of flavor evaluation was 4.1.

[Comparative Example 1]
A hollow fiber membrane was obtained in the same manner as in Example 1, except that the temperature of the outer tube of the double-tube spinneret was 100°C.
The membrane performance, polysaccharide clogging state, and intermediate water distribution of the obtained hollow fiber membrane were as shown in Table 1, and the average score of flavor evaluation was 3.6.

[Comparative Example 2]
38% by weight of a vinylidene fluoride homopolymer having a weight average molecular weight of 417,000 and 62% by weight of gamma-butyrolactone were dissolved at 150°C. This resin solution was held at 95°C in the range of (Tc + 20)°C to (Tc + 55)°C for 20 seconds under a pressure of 1.2 MPa, and then the outer tube was heated to 99°C. The liquid was sent to the type mouthpiece. The resin solution was discharged 4.7 seconds after entering the double-tube spinneret. While the resin solution was passed through the outer tube of the spinneret, a 90% by weight aqueous solution of γ-butyrolactone at 100° C. was simultaneously discharged from the inner tube of the double-tube spinneret. The discharged resin solution was solidified for 1 minute in a bath of 90% by weight of γ-butyrolactone aqueous solution at a temperature of 5°C. After solidification, the resulting film was washed with water and stretched 1.5 times in hot water at 95°C. The stretched hollow fiber membrane was washed with water, immersed in 30% glycerin for 2 hours, and air-dried overnight. After that, heat treatment was performed under steam at 125° C. for 1 hour.
The membrane performance, polysaccharide clogging state, and intermediate water distribution of the obtained hollow fiber membrane were as shown in Table 1, and the average score of flavor evaluation was 3.9.

[Comparative Example 3]
36% by weight of a vinylidene fluoride homopolymer having a weight average molecular weight of 417,000 and 64% by weight of dimethyl sulfoxide were dissolved at 120°C. This resin solution was held at 75°C in the range of (Tc + 20)°C to (Tc + 55)°C for 20 seconds under a pressure of 1.2 MPa, and then the outer tube was heated to 80°C. The liquid was sent to the type mouthpiece. The resin solution was discharged 4.8 seconds after entering the double-tube spinneret. While the resin solution was passed through the outer tube of the spinneret, a 90% by weight aqueous solution of dimethylsulfoxide at 75° C. was discharged from the inner tube of the double-tube spinneret at the same time. The extruded resin solution was solidified for 1 minute in a bath containing 90% by weight of dimethyl sulfoxide in an aqueous solution at a temperature of 5°C. After solidification, the resulting film was washed with water and stretched 1.5 times in hot water at 95°C. The stretched hollow fiber membrane was washed with water, immersed in 30% glycerin for 2 hours, and air-dried overnight. After that, heat treatment was performed under steam at 125° C. for 1 hour.
The membrane performance, polysaccharide clogging state, and intermediate water distribution of the obtained hollow fiber membrane were as shown in Table 1, and the average score of flavor evaluation was 3.8.

[Comparative Example 4]
38% by weight of a vinylidene fluoride homopolymer having a weight average molecular weight of 417,000 and 62% by weight of gamma-butyrolactone were dissolved at 150°C. This resin solution was held at 98°C in the range of (Tc + 20) °C to (Tc + 55) °C for 20 seconds under a pressure of 1.2 MPa, and then sent to a pipe whose outside was heated to 140 °C. After that, the liquid was sent to a double tube type mouthpiece heated to 100°C. 5.4 seconds after entering the piping heated to 140° C., the liquid was sent to the double-pipe mouthpiece. While the resin solution was passed through the outer tube of the spinneret, a 90% by weight aqueous solution of γ-butyrolactone at 100° C. was simultaneously discharged from the inner tube of the double-tube spinneret. The discharged resin solution was solidified for 1 minute in a bath containing an aqueous solution of 90% by weight of γ-butyrolactone at a temperature of 25°C. After solidification, the resulting film was washed with water and stretched 1.5 times in hot water at 95°C. The stretched hollow fiber membrane was washed with water, immersed in 30% glycerin for 2 hours, and air-dried overnight. After that, heat treatment was performed under steam at 125° C. for 1 hour.

The membrane performance, polysaccharide clogging state, and intermediate water distribution of the obtained hollow fiber membrane were as shown in Table 1, and the average score of flavor evaluation was 3.1.

The hollow fiber membrane of the present invention can be used for water treatment applications such as wastewater treatment, water purification treatment, and industrial water production, as well as applications such as food and pharmaceutical production.

Claims (3)

A separation membrane comprising a layer having a spherical structure,
the spherical structure contains a polyvinylidene fluoride-based resin, and the thickness L of the layer is 60 μm or more and 500 μm or less;
The separation membrane has a first surface and a second surface,
In the cross section of the separation membrane, among the regions separated by a width of 5 μm in the film thickness direction, the region Sp _max and the region Sp _min where the abundance of the polysaccharide component in the polysaccharide clogging state obtained in the polysaccharide clogging test described below is maximum and minimum. The polysaccharide component abundance ratio P _max /P _min is 10 ^0.8 or more and 10 ^2.5 or less,
Seven or more of the 5 μm wide regions exist between Sp _max and Sp _min ,
and a separation membrane in which Sp _max is closer to the first surface than Sp _min .
Polysaccharide occlusion test: An aqueous solution containing 2.0% by weight of a water-soluble polysaccharide component having an average dispersion diameter of 100 nm or more and 1000 nm or less and 5.0% by weight of ethanol was applied to the first surface at 2.0 m ³ /m ² /day. Filtration is performed at a constant flow rate by supplying to , and the filtration is stopped when the transmembrane pressure difference becomes 10 times the initial transmembrane pressure difference. Among the regions where the abundance ratio of the polysaccharide component is less than 3×P _min , there are 5 or more regions with an interval of 5 μm between Sp _(min−1) , which is the region closest to the first surface, and Sp _max . The separation membrane according to claim 1. Among the regions, the heat of fusion ratio Q _max /Q _min in the region Sq _max where the heat of fusion Q _i is the maximum and the region Sq _min where the heat of fusion Q i is the minimum expressed by the following formula (1) is 2.0 or more and 50.0 or less. hand,
7 or more regions with a width of 5 μm exist between Sq _max and Sq _min ,
3. The separation membrane according to claim 1, wherein Sq _max is closer to the first surface than Sq _min .

dq _i /dt: Differential scanning calorimetry change per volume in region _Si (J/K/cm ³ )
t: scanning temperature (K)